I don't keep a diary/journal per say, but lots of sketchbooks and notebooks with any good ideas I have throughout the day. I've also started writing down any weird dreams so I can recall them better lately--if I don't write them down immediately after I wake up (usually in the middle of the night) I'll usually forget I even had them.
I had a few journals between the ages of 6 and 9, though each of them would only last a few weeks before I stopped.
Then, when I was 11, I made a journal that I would write in everyday. I stopped when I ran out of pages, tho. I haven't attempted to keep a journal since then.
No, but maybe I should start. Especially for when I have a thought or an idea that I feel like I might want to come back too later and explore it possibly.